Hydrocarbon synthesis process



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lThe present invention relates to the 'manufacture of valuable synthetic products vby the catalytic conversion of gas mixtures containing hydrogen and carbon monoxide produced from gascous hydrocarbons .such as natural gas, refinery gases, etc. The invention is more particularly concerned with improvements in synthesis gas production, hydrocarbon vsynthesis operation and synthetic product recovery, Which cooperate t afford increases in yields of desired products and in thermal efficiency resulting in substantial savings in the synthesis of motor fuels and other valuable products on the basis of natural `gas or thelilre.

The catalytic synthesis of hydrocarbon oils and valuable chemicals Yfrom carbon lmonoxide Vand hydrogen has vbeen assuming increasing importance in recent years as a source of fuels and raw materials supplementing crude `oil resources. The process is generally based either on natural gas and other. gaseous hydrocarbons or on coal and .other carbonaceous solids as the raw material for the production of synthesis gas containing CO and H2 in the desired proportions. At the present time neither process type has advanced to a state of development at which the products of .the synthesis could be manufactured at a cost fully competitive with that of similar products recoverable from crude oil.

This is particularly true-for the synthesis of high octane motor 'fuels in the form of substan- .tially unsaturated hydrocarbons which may be produced from carbon monoxide and hydrogen inthe .presence of iron catalysts at elevated pressures. Extensive research and development Work Within 'the last ten years has demonstrated that the most desirable procedure with respect to thermal efIici-ency 'as well ag product yields and quality involves application of the so-called fluid solids technique wherein the catalyst is maintained ha the form of a dense highly turbulent mass of iinely divided solids iluidized lby upwardly owing gases to resemble a boiling liquid having `a Well defined upper interface. This technique, particularly when applied to iron-type catalysts, vnormally involves the use of relatively high pressures above about `250 lbs. and preferably of about 40G-600 lbs. per sq. in. to prevent catalyst car- 'bonization and iluidlzation difficulties.

One of .the obstacles in the path of using hydrocarbon gases as the basis for this type of synthesis operation has been the high cost of the ,production of high pressure synthesis gas. Other Adifficulties arose in connection with heat economy .and product recover 'with the result that a prod- :uct .competitive with that obtained from natural .petroleum could be produced only under the most ,favorable conditions of raw material, 'equipment and labor cost.

.t is; therefore, the principal object of the present invention cto provide-fan impro-ved proc- 4lclaims. (C1. 26o-449.6)

2 ess for the catalytic production oivaluable synthetic products from 'CO Eand H2.

A Ymore speciiic object of the `invention is to provide an improved process `vfor the catalytic synthesis of normally liquid hydrocarbons and other valuable products from CO and H2 produced from gaseous hydrocarbons such as natural gas, renery gas, -coal distillationgas',fetc.

Other and more specific objects and advantages `will appear hereinafter.

The inventionA will be fully 'understood -f'rom 'the 'following-detailed description referring `to fthe accompanying drawing wherein Figure l is a schematic flow planof a-complete plant for the production -oi `synthetic vfuels 'and chemicals on the basis of natural gas in .accordance with `the present invention Figures 2A, 2B vand 2C 'are more detailed views 4oi the ygas generation-synthesis andproductire covery sections, respectively; `of .the plant illusstrated in Figure 1; and

Figures 3 and 4 are nowsheets showing `:the dow oi steam and condensate AWater through the system.

Referring now -toFi'gure 1, natural gas as itis recovered'f-rom the Wellandspreferably .a natural gas of low-nitrogen content' may be passed substantiall-y at Well pressure -fromgas storage facilities A to a casinghead lrecovery*.system B fwherein hydrocarbons having .3 yor'inore carbon atoms are removed-by conventional methods, such as absorption, compression, and/or cooling to ,produce casing-headgasolineand a dry gas. The hy= drocarbon products removed from the gas in B may be fractionated in lC into .a C3, .a C4, and a 'C5-ifraction. `The VC: :and a portion of theA C4 fraction may vbe stored together `in U1to be used -as bottled gas Aor for similarpurposes, Whileanother portion -of the C4 fraction .and the 'C's and higher molecular Weight hydrocarbons 'may he passed on to be mixed YWith the gasoline :products of the process 'atl P.

The dry gas recovered from yplan-t B may have a ycomposition about .as follows:

Volume, per cent N2 0.1-0.3 CO2.- 0.1-0.5 CH4 92496 CzHs 3-5 CSI-I8 0.5-1.0 vClif-.i110 0.1

Natural 4gas of this type is combined with synthesis .tail rgas produced, as will appear more clearly hereinafter, fand. the `,gas mixture is Asup.- plied to a synthesisfgas generation stage D. Technicallyl pure .oxygen :of about f-997% purity is produced in oxygen plan-t- E by the air ,lique- Vfaction technique.l vSynthesis gas :generation in stage D takesfplace by incomplete/combustion with the oxygen :suppliedto produce a mixture consisting for :theY most` .part of hydrogen and 3 carbon monoxide having an Hz/CO ratio of between 12, preferably of about 1.3-1.7.

The synthesis gas so produced is cooled by heat exchange with other process materials and supplied at about synthesis temperature and pressure to synthesis plant F which, in accordance with the preferred embodiment of the invention, is operated as a fluid catalyst type synthesis system using iron-type catalysts. The feed gas is preferably admixed with recycled tail gas prior to its admission to the synthesis reactor. Broad ranges of operating conditions for this type of hydrocarbon synthesis include temperatures of about 550-800 F., pressures of about 150-650 lbs. per sq. in., total gas velocities of about 0.3-1.5 ft. per sec., at catalyst particle sizes of about 20-200 microns and apparent densities of about 50-150 lbs. per cu. ft. as well as total gas throughputs vof about l0 to 1,000 V./Hr./W. (defined as the standard cu. ft. of total gas feed per hour per lb. of carbonand oxygen-free catalyst in the reaction space). The volumetric ratio of recycle gas to fresh feed gas may be maintained within the approximate range of 0-6. Synthesis plant F also includes conventional means of separating the reactor effluent into normally gaseous constituents, an oil layer and an aqueous layer containing also oxygenated products.

The normally gaseous constituents and the oil layer are sent to absorption plant G after the amount of gas required for recycle has been split off the stream of gaseous constituents. 1n plant G the gaseous constituents are scrubbed with the product oil in a manner which will be explained in detail below with reference to Figure 2C. Essentially 3 separate streams leave absorption plant G. A gas stream comprising essentially hydrocarbons having 2 carbon atoms per molecule or less, nitrogen, hydrogen, carbon monoxide and carbon dioxide, is partly recycled to synthesis gas generation stage D as mentioned above and vpartly passed to fuel gas storage facilities H. A rstream containing hydrocarbons having 3 or 4 carbon atoms per molecule is passed to a poly- -merization plant I wherein the oleiinic hydrocarbons may be polymerized by conventional polymerization processes in the presence of polymerization agents such as sulfuric acid or phosphoric acid carried on suitable supports, such as xieselguhr or the like, to form hydrocarbons of the motor fuel boiling range. Gaseous hydrooarbons remaining unpolymerized may be combined with the gas stream leaving absorption plant G. Polymer product containing some C4 hydrocarbons may be withdrawn from plant I to storage L to be eventually combined with other gasoline product in mixing plant P. Polymer bottoms boiling above the motor fuel range may be stored in M and/or combined with other products of similar boilingrange in fuel oil facilities Q. A third stream containing hydrocarbons having 5 or more carbon atoms per molecule is passed from absorption plant G to a catalytic treating plant K wherein these materials may be refined by catalytic cracking, hydroforming, or similar renning operations. The products of such catalytic treatments are fractionated into a gas stream containing hydrocarbons of 4 or less carbon atoms per molecule which is reprocessed in the above-mentioned absorption plant G, motor fuel fractions containing C5 and higher molecular hydrocarbons boiling up to about 400 F. which may be combined with the gasoline stock in P, and an oil having a boiling range above 400 F.

which may be sent to fuel oil storage Q. intermediate storage facilities M, N, and O may be provided for polymer bottoms, catalytically treated gasoline and catalytically treated fuel oil, respectively.

Returning now to synthesis plant F, the water layer recovered from the reactor effluent is seed to a recovery plant R for the separation of alcohols and acids from the water layer by conventional chemical and physical means.

Having thus described the general outline of the process of the present invention, its novel features and the objects and advantages accomplished thereby will be best understood from the following more detailed description of individual sections of the system illustrated in Figure l, wherein reference will be made to Figures 2A, 2E, and 2C.

The system illustrated in Figures 2A, 2B and ZC will be described using the production of about 10,000 barrels of motor fuel and fuel oil from a dry natural gas of the type referred to above having about the following composition:

Volume, per cent N2 0.20 CO2 0.30 Cil-'f4 94.57 C21-I6 4.14.- CeH 0.75 C4'1o 3.04

-Referring now more specifically to Figure 2A, about lili MM SCF/ SD (million standard ou. ft. per stream day) of this dry natural gas are supplied at a temperature of about 600 through line i to line 5. Simultaneously about 46 MM SCF/SD of recycle gas obtained in the synthesis section of the system as will appear more clearly hereinafter are added through line 3 to line 5. The gas mixture is passed through line 5 at a temperature of about 70 F. and a pressure of about 495 lbs. per sq. in. to a heat exchanger le wherein its temperature is raised to about 920 F. in indirect heat exchange with synthesis gas produced in synthesis gas generator 25. For this purpose, heat exchanger l0 may have a capacity of about 172 million B. t. u. per hour and a heat exchange surface area of about 14,000 sq. ft. The preheated feed gas is passed through line l2 at a pressure of about 465 lbs. per sq. in. to burners it arranged in a lower portion of generator 2e. The feed gas is mixed in burners lil with about 81 Mil/ SCF/SD of oxygen of 95% purity produced in oxygen plant lli by air liquefaction and fractionation. rlhe oxygen is compressed in a compression stage i5 comprising preferably 3 three-stage centrifugal oxygen compressors, to a pressure of about 483 lbs. per sq. in. and passed at a compressor outlet temperature of above 350 preferably about 430 F. (for an Q2 inlet temperature of about 100 F.) to heat exchanger il' wherein the temperature of the oxygen is raised to about 80.1 l. in indirect heat exchange with synthesis gas produced in generator 20. The temperature differential between oxygen inlet and outlet temperatures of this compression stage should generally be about 200-400 F. Heat exchanger il may have a. capacity of about 24 million B. t. u. per hour and heat exchange surface of about 2,730 sa. ft. The preheated oxygen is supplied through line 20 to the generator burners it at a temperature of about 800 F. Oxygen heat exchanger il may be a low duty preheater of the type specified as a result of the relatively high outlet temperature of oxygen compressors i5 acca-'tee Oxygen compressor intercoolers Synthesis gas generator 25 consists of a lower combustion section 2.7 andan upper .boiler section 2'9 formed bybrick or refractory Walls '30. A metal shell 3i is provided toperrnit operation at the elevated pressurespecied. Boiler section 29 contains a bundle of preferably vertical boiler tubes 32 topped by a steam .header 34 and Vclosed at the bottom by a thermally insulated boiler tank 36. Boiler section 2.3 is vshown in the drawing as having a diameter substantially smaller than combusti-on section 21. The purpose of this difference in diameters is a substantial increase -of the gas Velocity in the -boiler section as compared tothat in the heater section in order to take advantage of a corresponding increase in the heat transfer coeiiicient at the vhigh pressures involved Without interfering With the relatively low gas velocities which should be maintained in combustion section 2'! as a function of the velocity of name propagation. If desired, metalshell 3| may be surrounded by a cooling Water jacket (not shown) particularly in the .combustion section to protect the metal from excessive temperatures.

A generator of the type .illustrated in the drawing may be operated atpressures of about 400- 600 lbs. per sq. in., temperatures of about 2,000"- 25'00"` F. in the combustion section, boiler section outlet gas temperatures of about v $-1200 F. and gas velocities of .about 8-1'2 ft. per'sec. in the combustion section and about lD-'200 ft. yper sec. in the boiler section. Operating conditions fpreferred for the specific example hereinvolved are u listed in the following table.

Synthesis gas :generator Combustion section:

Temperature, FHr 2260 Pressure, p. s.'i.g li165 1.-]3., ft 10.25 Height, ft. 27 Outlet gas vel., ft./sec '9-.5 Reaction time, sec. 2.8-}-

Boiler section:

Temperatures, F.:

' Inlet 2260 Outlet 1000 Pressure drop, p.'s. 4.6 LVD., it. 13.0 Height, ft. 40.0 Gas velocity, ft./sec.:

lnlet 195 Outlet 105 Boilera'rea, ft2 5280 Tube spacing, in. sq 1.375 Tube' O.D.,in 1;0 Heat ux,=B. vt. 'n./hn/ftz':

-Axlerag'e' "i v89,000 V.Maximian-1 v -1'5"6,f000

6 Ifhese conditions may be maintained by supplying'about L92,700 gals. `of water per-hour at about 470 F.'and a pressure of Iabout`625 lbs. .per sq. inpthroughline 38 to steam drum 40from which wate-ris Withdrawn through line 42 Aand supplied to boiler tank 35. A vmixture of steam .and condensate leaving boiler tubes 32 is returned through line 44 tolsteam drum High pressuren saturated steam vmay be Withdrawn from steam ldrum lillthrough line te ata rate of about '628,000 lbs. per y.hou-r. Use of high synthesis gas pressure in the combustionan'd boiler section of the generator results in 4much more emcient utiliza-tion of the boiler surface'than is obtainable atv relatively'low pressures of,'say, about .atmospheric. For example, the heat transfer coeliicient is substantially increased, affording an average heat .flux of about 7.5 times as great .as that obtained in atmospheric pressure operation. Methane conversion in .combustion section 2l may be readily maintained at about i-92%.

The synthesis gas produced isl Withdrawn through line 50 `and passed at a temperature of about 10`00 F. vpartly to heat exchanger It' Aand partly to heat exchanger Il wherein some of its heat is transferred to the hydrocarbon feed gas and the-oxygen, respectively, as described above. The cooled synthesis .gas is withdrawn from heat exchanger I1 at a temperature of about 630 F. and from heat exchanger l0 at a temperature of about 380 F., combined .in line 52 to assume a temperature of about 425 F. and passed at a pressure of about 450 l'bs.per sq.in. to a boiler feed preheater 5LB wherein it is cooled in heat exchange with about 1,000,000lbs. per hour of Iboi-ler feed Water fed at a temperature of about -G F. `to assume a temperature of about lil. A heat exchanger having a capacity of about 154 million E. t. u. per hour and a heat exchange surface of about 13,000 sq. it. is .adequate for this purpose and to yield a boiler feed having a tei perature of about 275 F. By coolingV the synthesisgas in heat-exchanger -'l downonly to 175 F. rather than to the substantially lower temperatures which are conventional, the Water content of the synthesis .gas is increased from, say, about 0.22 to about 1.5%. However, some 20 million B. t. u. per hour of additional heat are made available fcrsteam production in .the synthesis section as a result of this higher synthesis gas temperature. Any potential detrimental effect of the increased -Water vapor 'content on the vsynthesis reaction may beovercorne by a slight increase of the ratio of recycle gas to fresh feed gas supplied to the synthesis reactor. The cooled synthesis gas issupplied through line 56 .at a `pressure of about 450 lbs. per sq. in. to a separater 5B vwherein condensed Water is separated from the gas. About 72,000 lbs. per hour of condensed Water are removed from separator 58. The synthesis gas now free of liquid water is passed through line 5i! in an amount of about .370 MM SCF/SD to the synthesis rsection of the system which is illustrated in Figure 2B.

Referring now to Figure 2B, the synthesis gas inline 6i) is admixed With about 550 MM SCF/'SD of synthesis tail gas obtained by separation of .normally liquid products from the synthesis reactor reiuent as will appear more clearly hereinafter, and supplied through line 52. The gas mixture ows at a temperatuer of about 140 F. .and a ,pressure of about 4.40 lbs. per sg. in. .through yline 64 to heat exchanger t5 wherein itsf-temperature is raised to about 275 F. in heat exchange fwith 'the' total effluent" from-'synthesis reactor l0. A heat exchanger having a capacity of about 125 million B. t. u. per hour and a heat transfer area of about 22,000 sq. it. is sufficient for this purpose. The gas mixture is then supplied through line 01 at a pressure of about 435 lbs. per sq. in. to synthesis reactors 10 in an amount of about 930 MM SCF/CD.

Synthesis reactors l may be of a design conventional for fluid operation and provided with a distributing grid i2 in its lower portion and gas-solids separating means such as cyclones 14 in its upper portion. Each reactor contains about 145 tons of an iron-type catalyst having an average particle size of about 32 microns. The dimensions of the reactor are such that an inlet gas velocity of about 1.4i ft. per sec. and a gas velocity of about 1.1 ft. per sec. at the top of the fluidized catalyst mass 'm is maintained when the amount of synthesis gas nowing through line Si is distributed over 6 reactors of the type of reactor l0, operated in parallel. For this purpose, the cylindrical section of each reactor may have an inner diameter of about 1l ft. and a height of about 55 ft. Each reactor is provided with a cooling coil having a heat transfer area oi about 3,000 sq. ft. A total of about 92,000 gals. of water of 470 F. is supplied to reactors 10 to maintain therein a temperature of about 650 and to produce a total of about 620,000 lbs. per hour of saturated steam at 625 lbs. per sq. in. pressure. Assuming reactor dimensions oi' the type specified above, this may be accomplished by conventional boiler tube arrangements.

The preferred iron catalyst for the process of this invention is a pyrites ash sintered at a ternperature of about 12001600 F., ground to a particle size of about 100 microns and reduced with hydrogen at 900 F. and 425 lbs. per sq. in. pressure to an oxygen content of about calculated on iron. In the course of the synthesis reaction, the oxygen content of the catalyst increases, carbon is deposited and considerable catalyst disintegration takes place. It is desirable to maintain the oxygen content of the catalyst at about the carbon content at about 34%, based on iron, and the average particle size at about 32 microns. This may be accomplished by supplying a total of about 50,000 lbs. per day of freshly reduced sintered catalyst of 100 micron particle sise through line i8 to reactors l0. The catalyst hold-up of reactors 'i0 may be maintained substantially constant by catalyst entrainment in the reactor efiluent. If desired, catalyst iines separated in separator lli may be withdrawn from the system through line 80.

Total reactor eiiluent is withdrawn from reactors s0 through line 52 at a temperature of about 550 F. and a pressure of about 400 lbs. per sq. in. and passed to a heat exchanger 85 wherein it is indirectly cooled to a temperature of about 470 E'. by indirect heat exchange with the total boiler feed water of about 272 F. containing that Withdrawn from heat exchanger 54 through line 55. About 1,250,000 lbs. per hour of boiler feed ci 470 l'. are recovered through line S1 from heat exchanger t5 which may have a capacity of 265 million B. t. u. per hour and a heat eX- change surface area of about 18,430 sq. ft. The reactor eliluent leaving heat exchanger 05 through line 5s is admixed with about 200 barrels per day ci gas oil supplied through line 00 and the miX- ture is passed at a temperature of about 375 F. to heat exchanger 55 wherein part of its heat is given off to the synthesis feed gas as previousiyv described.l Reactor effluent now enters at a temperature of about 265 F. and a pressure of about 395 lbs. per sq. in. through line 02, a cooler 04 wherein it is cooled to a temperature of about F. Cooler 04 may have a capacity of about 276 million B. t. u. per hour and a cooling area of about 29,000 sq. ft. Some 14,500 gals. per minute of water of 83 F. may be supplied to cooler 04 through line 25 and withdrawn through line 08 at a temperature of about 120 A mixture of gaseous and liquefied reaction products is withdrawn from cooler 05 through line |00 at a temperature of about 100 F. and supplied at a pressure of about 390 lbs. per sq. in. to separator |02 in which a separation of the reaction products into a lower aqueous layer a, an upper oil layer o, and normally gaseous products takes place. The aqueous layer is withdrawn through line |05 to be further treated as will appear hereinafter. The oil layer is passed through line |06 to an absorption plant ||0 wherein it is further separated into C2 and lower boiling gases, Cas-C4, and C5i. A portion of the normally gaseous products passes from separator |02 through line I8 without a substantial pressure drop to plant H0 details of which are illustrated in Figure 2C. A portion of the oil layer, amounting to about 2.5 gals. per minute, may be continuously circulated from the bottom of the oil layer through line l i2 and rotary filter IH for the recovery of suspended catalyst ines. Other methods for handling the solids carried over may be employed, such as filtration of the liquid bottoms separated in the vaporizer handling the feed to the product treater, or separation and filtration of the condensate plus oil at the outlet of heat exchanger 05.

Of the 650 MM SCF/ SD of tail gas separated in separator |02, about 560 MM SCF/SD are passed through line ||0 to be recycled by recycle gas compressor H8 through lines 02, 04 and 0l to reactors "i0, The gas in line |6 is under a pressure of about 385 lbs. per sq. in. Of the tota-l tail gas obtained in absorption plant H0, about 75 MM SCF/SD are withdrawn through line |20 and about 11 MM SCF/SD through line |22 as will appear more clearly hereinafter. The gas in line |20 is under a pressure of about 3'70 lbs. per sq. in. and that in line |22 under a pressure of about 200 lbs. lper sq. in. Some 35 MM SCF/ SD of tail gas may be withdrawn from line |20 through line 12| and about 5 MM SCF/SD from line |22 through line |20 for fuel purposes. About 6 MM SCF/ SD of tail gas from line |22 are combined with the gas in line 20 to make up a total of about 46 MM SCF/ SD which may be compressed in recycle compressor |25 to about 495 lbs. per sq. in. pressure and returned through line l2? to lines 3 and 5 as the generator recycle stream referred to above. The gas in line |22 is particularly well suited for recycle to synthesis reactor i0 as a result of its high CO2 content which may amount to about '70%, more or less. It may be desirable, therefore, to recycle all or a portion of the gas in line |22 through line |20 to reactor l0. Liquid products are withdrawn from adsorption plant |0 through line |30 and passed either to storage or to any further catalytic treatment of the type referred to above in connection with plants i and K of Figure l.

One of the major diiferences of the design of the synthesis section illustrated in Figure 2B from conventional designs resides in the fact that no reactor overhead gas-oil scrubber and concomitant steam boiler is arranged on line 32. The purpose of this scrubber was to prevent fouling tl' of the overhead coolers by the entrained catalyst at the point of primary condensation of the product. It has been found, however, that no condensation actually occurs until the reactor veiiluent gases are cooled to temperatures approaching 300i F. Therefore, advantage is taken in accordance with the present invention of the higher temperature level heat in heat exchanger 85 by introducing the 650 F. reactor eiiiuent directly to this exchanger. A substantial reduction in exchanger area may be realized in this manner. imilarly, the temperature of the gas entering heat exchanger 05 is higher than in conventional cases. This factor, combined With the increased heat capacity of the gas stream resulting from the combination of fresh synthesis' gas with recycle gas as the stream entering heat exchanger 65, allows a substantial increase in the heat load for exchanger 65 with little decrease in heat flux. While condensation of oil and Water products takes place in heat exchanger 55, fouling of the tubes of this exchanger is prevented by spraying a small amount of gas-oil through line into the exchanger inlet as described above. This amount of oil is suiicient to give a solids concentration of less than 0.5 lb. per gal., based on an entrainment rate of .00 lb. per cu. ft. in the reactor eluent stream entering cyclones 'F4 operating at an efliciency of about 90% each. The slurry formed in heat exchanger 65 flows to separator |02Y along with the synthesis products as described above.

Referring now to Figure 2C, absorption plant ile is illustrated therein to comprise essentially an absorber |35, a deethanizer |40, a. debutanizer 00, a lean oil still |90, and a stripper 220, which may be operated substantially as follows. v

VThe product oil layer from section F of Figure 1 passes through line I 06 (see also Figure 2B) into the stripper tower 220 Where 05+ hydrocarbons are removed at the bottom and passed through a pump to be combined with the debutanizer bottoms and sent to plant K of Figure 1 through line |30. Product gases from section F of Figure 1 pass through line |08 -into the absorber |35 where 04+ and most of the C3 hydrocarbons are absorbed in oil. The rich oil leaving the absorber bottom is combined with the stripper" overhead and sent to the deethanizer |40 where C2 and lighter hydrocarbons pass overhead through line |20. Tail gas consisting of Cz and lighter hydrocarbons separated in absorber |35 from the synthesisv product gases from section F is also removed through line |22. v

Cs-lproducts in absorber oil are withdrawn from ythe bottom of deethanizer |40 and Venter the lean oil still i90 Where open steam strips out Ca-ihydrocarbons and lean oil is Withdrawn from the bottom to be cooled and reused in the absorber 35 `and deethanizer |40. The C3| products leave the lean oil still |80 and are cooled by indirect heat exchange with boiler feed Water followed by compression before entering the debutanizer |60. From the top of this column Cad-C4 pass through line |10 to plant I of Figurel.

C21. and lighter hydrocarbons produced in plant K enter the deethanizer Where the lean oil recovers C3 and C4 hydrocarbons. A fired reboiler |05 is used to provide heat to the deeth'anizer |40; alternate connections may be.k provided such that hotoil may be circulated directly from the red reboiler |55 to the cooler I0! on the lean. oil

still overhead stream. This alternate circuit .10` maybe ,usedv for heating feed Water during the start-up period.

The C5| hydrocarbon product withdrawn through line |30 may be catalytically treated in treating plant K. While bauxite treating mayl be used, a treatment Withsilica alumina cracking catalyst'at about 950 F. is preferred. Fluidtype catalytic cracking systems of conventional.

design, yincluding reactor and regenerator vessels may be used and operated at the conditions specied below.

Treater vessels Because of the high olefin content of the fresh feed to the polymerization plantI, of about 86%, a "relatively high recycle stream Yfrom the top of the polymer stabilizer is required to keep the concentration of olens in the total feed to the polymerization reactors at the desired level. A total feed rate of about 11,900 barrels per day is adequate for this purpose. Because it is desired to recover all of the butanes for pressuring the gasoline in P of Figure 1 no debutanizer is required. Also, because the fresh feed tothe polymer plant is relatively pure, no sul.- fur removal facilities Vare necessary.

The process steam produced inl synthesis gas generator 25 and reactor 'l0 is sufficient to supply all of the integrated steam requirements of the process. All of the steam is produced at about 625 lbs. per sq. in. pressure and superheated to about 750 F. in a separate gas-fired furnace, while the 200 lbs. per sq. in. boiler nor- Inally included in the oil scrubber system has been eliminated together with the oil scrubber system. The flow of Water and steamthrough the plant and the recovery of condensate are illustrated in Figure 3, which is largely selfexplanatory. It may be sufficient to note with reference to Figure 3 that all steam is generated at 625 lbs. per sq. in. pressure While low pressure steam requirements are fulfilled using exhaust from steam engines. condensate at atmospheric pressure is collected separately from vacuum condensate which comes from turbine condensers. Both condensate streams are combined and pumped through the preheaters to the boilers. It will` be observed that in addition to air and oxygen compressor turbines, only the following drives require steam condensers:

Reactor recycle booster, 8 Propane refrigeration compressor Utility air Cooling Water pumps These condensers utilizek salt Water at 83 F. andv a. maximum outlet water temperature of 104 F. All of the 200 lbs. per sq. in. and 125 lbs. per sq. in. saturated steam is provided by bleeding from air compressor turbines as shown in Figure 3. With the exception of the turbines noted which have steam condensers, the remainder of the turbines discharge to the 15 lbs. per sq. in. steam main. About 28,000 lbs. per hour of the superheated high pressure steam is throttled to 200 lbs. per sq. in. for process strip.- ping purposes in lean oil. still 190.

No continuously operating fired boiler is required in the Adesign illustrated by the drawings in contrast to conventional designs because a ll red reboiler l5@ is used on the bottoms of deethanizer hill in absorption plant H0. This arrangement reduces the total steam requirement of absorption plant H by as much as 100,000 lbs. per hour as compared to prior art designs. In addition, the elimination of the 200 lbs. per sq. in. steam boiler after synthesis reactor 'l0 has made it possible to utilize that heat in pre'- heating boiler feed Water for the production of 625 lbs. per sq. in. steam. Greater eniciency is thus realized by supplying any 200 lbs. per sq. in. steam required by bleeding the high pressure steam through oxygen plant air compressor turbines. Since no continuously operated fired boiler is required, a relatively cheap steam boiler may be provided for temporary starting-up purposes.

Such a furnace may also be designed for a disposal of the product Water layer when the chemical recovery sections are shut down. The boiler may be so designed as to produce enough steam to supply one complete section of the oxygen plant and one oxygen compressor and thus provide a means for starting the synthesis gas generator and boiler at full operating pressure. This arrangement makes it possible to design gas generator Z for operation at high pressures only.

Since all of the steam for normal plant operation is provided by the reactor and generator Waste heat boilers, it is necessary in starting up to generate suilicient steam to get one oxygen plant unit into operation and thereby initiate Waste heat steam production in the synthesis plant.

The oxygen lrom this unit may be compressed to :l

full generator pressure in order to obtain high heat transfer rates in the generator boiler. For this purpose, it is desirable to provide a special lovv cost start-up boiler burning natural gas and producing about 185,000 lbs. per hour of saturated steam. In starting up, boiler feed Water may be preheated in absorption plant Il@ by circulating oil at about 500 E'. from iired reboiler 55 through overhead boiler `feed preheater i9! of lean oil still E99. The saturated steam may be superheated to 750 F. in the iired superheater (Fig. ure 3), which is provided for normal plant operation. The start-up boiler hook-up is shown in Figure 4 in a manner similar to the flow of Figure 3.

The total oxygen supply may be generated in 3 plant units, each with a separate air compressor and oxygen compressor. The 185,000 lbs. per hour of steam mentioned above is suicient to start one oxygen unit to full capacity and operate all the necessary auxiliaries. This constitutes the iirst increment of starting-up and may be provided in order to put one oxygen unit in operation as rapidly as possible.

The next step is to make steam available for oxygen compression by reducing the flow of steam to the air compressor turbine, such that only 55 of the rated compressed air is available to the oxygen plant unit. Under these conditions, the plant Will produce about 50% of its designed oxygen output. The steam requirement for air `compression may then amount to about 107,000 lbs. per hour. Thus by backing off on the steam supply to the air compressors, it is possible to provide about 54,000 lbs. per hour of steam for oxygen compression. This is sufficient to operate one oxygen compressor at 50% of its rated capacity. Consequently, it is possible to provide, at high pressure, one-sixth of the total oxygen capacity using the steam made avalabl@ @S 1- scribed above. Synthesis gas generation is now initiated and saturated steam from the generator Waste heat boiler becomes available. Thereafter, suiiicient steam is being produced to start one of the synthesis reactors.

The plant may then be brought up to full operation by steps in which steam as it becomes available from Waste heat boilers is used to start additional oxygen plant units. Synthesis gas generation may be increased at increments or onesixth total capacity and may be sent at 650 F. to one of the 6 synthesis reactors 'lil wherein additional steam is generated by the synthesis reaction. The steam supply outlined above has been found t0 be more than adequate after waste heat steam has once become available from the generator and reactor.

As previously indicated, the aqueous layer removed through line IM may be worked up by chemical and physical means to recover alcohols, acids, and other Water-soluble synthetic chemicals. When none or" the other soluble chemicals are Worth recovering except for such alcohols as may be blended into gasoline, a Water-alcohol mixture may be distilled oil" the acid product water whereafter treated synthetic gasoline, in cluding polymerization product, may be used to extractively distill the alcohols. The acid water may be disposed of by preheating with excess steam followed by combustion with excess tail gas from absorption plant H0. In this case, boiler feed water make-up requirements may be supplied by water condensed from synthesis gas and Withdrawn from separator 58 augmented by about 40 gals. per minute from evaporators of acid Water.

When alcohols are merely dehydrated for blending into gasoline and Water-soluble acids are recovered, a considerable reduction may be eifected in the steam requirements for chemical recovery compared with the case where both alcohols and acids are recovered in the form of pure chemicals.

At the conditions specified for the above examples, about 160,000 lbs. per hour of water may become available as extractive product Water layer leaving the acid recovery plant and containing about 0.03% of acetic acid. Upon neutralization, this stream may be used to make up for the total plant condensate losses which may amount to about 156,000 lbs. per hour. Any deficiency which may arise from additional losses incurred through boiler blow-down to maintain solids concentration below about 0.25% may be made up by utilizing Water 4condensed from the synthesis gas and removed from separator 55. While some carbon may appear in this Water, a substantial proportion will be available in a carbon-free form because the synthesis gas is cooled in exchanger 54 which may have several series stages of exchangers, so that most of the carbon may be eliminated by separating Water between these stages, and relatively pure water is condensed in the last stage.

About 40 MM SCF/SD of oil-scrubbed synthesis tail gas will be available for fuel purposes from the system described above in addition to the gas recycled to the generator. This tail gas consists of overhead streams from the absorber and deethanizer of absorption plant lid. It includes all gas produced in the process lighter than propylene and in addition quantities of propylene andL propane equivalent to about 20% of the C3 hydrocarbons produced in the syn- The total heating Value of vthis "gasis'about 590 million B. t. u. per hour. The following tabulationfsummarizes the heat and fuel requirements of the system illustrated in the drawing.

. Heaty Out- Fuel Gas Percent Unit put, MM Input, MM ol Tail B. t. u./Hr.` B. t. u./Hr Gas Steam Superbes-ter. 222 v 288 l 48.7 Absorption Plant '132v 171 Y 28.9 Treating Plant 18 3.5 5. 9

It will -be seen that there is excess tail gas available equivalent to almost 100 MM B. t. u. per hour. I-n order to illustrate the production elliciency of the system illustrated by the drawing, the selectivity ofY carbon in the COA converted to liquid products is tabulated below.

Product constituent: Barrels per day C3 hydrocarbons 1772 C4 hydrocarbons 1860 Cri-400 F. hydrocarbons 7250 400 F.| hydrocarbons 2210 Oxy comp. (in H2O) 1820 1 1 As ethanol equivalent of carbon in water layer.

A treatment of the 9,460 B/D of C+ hydrocarbon product in catalytic treating plant Ii as described above will yield the following normally liquid or readily liquefiable products:

Product constituent: Barrels per day C3 hydrocarbons 490 Ct hydrocarbons 600 Cs-lOOo F. hydrocarbons 6400 400 F.-[ hydrocarbons 1420 The Reid vapor pressure of the treated C5-400 F. product is about 6.2 lbs. per sq. in. and its research octane numbers are about 94.7 clear and 98.9 with 2 c. c./gal. of tetraethyl lead.

The C3 and C4 constituents of the synthesis product polymerized in plant I as described above are as follows:

Constituent: B/SD C3H6 1630 CsI-Ia 281 04H8 2136 C4H1o 335 Plant I converts about 95% ofthe olens to polymer gasoline and about '5% to polymer bot- 14 f toms. The resulting yields Vand product quality of this polymerization are tabulated below:

Research O. N.

B/SD RVP n C1 +2 cc.

Polymer 2, 625 2. 5 97. 4 100.3 Bottoms 138 Because there is no debutanizer included in the polymerization plant, the above C4s are actuallyv recovered in combination with the polymer. The C3s are separated in the stabilizer, which provides recycle gas for the polymerization reactors, and the net quantities (of Cas) indicated above are discarded as part of the synthesis plant tail gas. l

In addition to these products, substantial amounts of gasoline hydrocarbons may be recovered from the natural gas in casinghead recovery plant B of Figure 1 about as follows:

Constituent: B SD C3 696 The C5-400 product from vthe treating plant may be blended With the polymer and with the 05+ from the casinghead plant to form the gasoline base stock. The polymer stream in this'blend includes the unconverted butylenes and the normal butane from the polymerization plant. The gasoline then may be brought up to a Reid vapor pressure of 10 p. s. i. by the addition of the required amount of C4s recovered in the casinghead plant. The octane number of the resulting gasoline may be raised to 97 research by the addition of tetraethyl lead. The following tabulation summarizes the yields of all products.

Products, B/SD:

Gasoline, 10 lb. RVP 10,457 O. N. Res. Cl 95,7 TEL Vfor 97 O. N., cre/gal 0.34

Gas oil 1,558

Alcohols, recovered 913 Acids, recovered (M lb./SD) 562 (203.6)

LPG 1 929 1 Includes excess C4s and all Cs from casinghead recovery plant.

An increase in gasoline yield of 15% over conventional procedure has been realized and appreciable increases in the other products have also been obtained. The synthetic products in the above gasoline amounts to 90.5%. If recovered casinghead is not blended with the synthetic products in the gasoline, extraneous "rLCi amounting to 481 B/SD will be required to pressure the gasoline. The resulting gasoline yield, having a research octane number of 96.5, is 9948 B/SD. The process of the invention also has been found to aiord a yearly return on total invest- `ment about 40-45% greater than that of previous designs.

What is claimed is:

1. The process for producing valuable synthetic products from a normally gaseous hydrocarbon which comprises subjecting said hydrocarbon in a synthesis gas generation zone to partial thermal combustion with free oxygen at a temperature of about 2000 to 2500 F., operating exclusively at a pressure or" above about 400 p. s. i. g. to produce a gas mixture containing H2, CO and Water vapor, cooling said gas mixture in indirect heat exchange with H2O, said hydrocarbons, and said oxygen substantially at said pres sure to a temperature not substantially below 1750 F. and removing as liquid water the H2O condensed therefrom at said temperature, reheating said gas mixture to a temperature of 250 to about 300 F., contacting said reheated gas mixture with a dense turbulent mass of a subdivided uidized iron-type catalyst in a synthesis Zone substantially at said pressure, indin rectly cooling said catalyst with Water to maintain a synthesis temperature or about 609 to 700 F., withdrawing a gasiform eiiluent from said synthesis zone at substantially said synthesis temperature and pressure, cooling said eiiiuent exclusively in indirect heat exchange with water to a temperature within the range of about 350C to 470 at which substantially no liquid condensation takes piace, further cooling said eiiiuent by adding thereto a minor amount of a heavy oil boiling above said latter temperature, passing the resulting mixture of liquid and vapors in indirect heat exchange with said gas mixture of not below about 175 E'. to reheat said mixture to about Z50-300 F., and nally condensing normally liquid products from said efiiuent.

2. The process according to claim 1 in which all the gas streams compressed icr feeding into said synthesis gas generation zone and said synthesis zone, including hydrocarbon, free oxygen and recycle gas streams, are at substantially room temperature when fed to compression.

3. The process of claim 1 in Which steam required to maintain the process in operation is generated exclusively by indirect heat exchange with the effluent gas from said generation zone and With the fiuidized catalyst in said synthesis zone at a high pressure, low pressure steam requirements being supplied as exhaust steam from stages using high pressure steam.

4. The process of claim 1 in which said cooling of said gas mixture from said synthesis gas generation zone to a temperature not below 175 F. is carried out in stages, water condensed in successive stages is removed, and water recovered from the last stage is used to produce steam required for the process.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,253,607 Boyd et al Aug. 26, 1941 2,264,427 Asbury Dec. 2, 1941 2,274,064 Howard et al Feb. 24, 1942 2,324,172 Parkhurst July 13, 1943 2,360,463 Arveson Oct. 17, 1944 2,400,075 Claussen May 14, 1946 2,436,957 Eastman Mar. 2, 1948 2,461,065 Kemp, Jr. Feb. 8, 1949 2,464,532 Sellers Mar. 15, 1949 2,470,216 Keith May 17, 1949 2,472,219 Lyons June 17, 1949 2,476,788 White July 19, 1949 2,527,846 Phinney et al Oct. 31, 1950 2,533,666 Gunness Dec. 12, 1950 

1. THE PROCESS FOR PRODUCING VALUABLE SYNTHETIC PRODUCTS FROM A NORMALLY GASEOUS HYDROCARBON WHICH COMPRISES SUBJECTING SAID HYDROCARBON IN A SYNTHESIS GAS GENERATION ZONE TO PARTIAL THERMAL COMBUSTION WITH FREE OXYGEN AT A TEMPERATURE OF ABOUT 2000* TO 2500* F., OPERATING EXCLUSIVELY AT A PRESSURE OF ABOVE ABOUT 400 P.S.I.G. TO PRODUCE A GAS MIXTURE CONTAINING H2, CO AND WATER VAPOR, COOLING SAID GAS MIXTURE IN INDIRECT HEAT EXCHANGE WITH H2O, SAID HYDROCARBONS, AND SAID OXYGEN SUBSTANTIALLY AT SAID PRESSURE TO A TEMPERATURE NOT SUBSTANTIALLY BELOW 175* F. AND REMOVING AS LIQUID WATER THE H2O CONDENSED THEREFROM AT SAID TEMPERATURE, REHEATING SAID GAS MIXTURE TO A TEMPERATURE OF 250* TO ABOUT 300* F., CONTACTING SAID REHEATED GAS MIXTURE WITH A DENSE TURBULENT MASS OF A SUBSDIVIDED FLUIDIZED IRON-TYPE CATALYST IN A SYNTHESIS ZONE SUBSTANTIALLY AT SAID PRESSURE, INDIRECTLY COOLING SAID CATALYST WITH WATER TO MAINTAIN A SYNTHESIS TEMPERATURE OF ABOUT 600 TO 700* F., WITHDRAWING A GASIFORM EFFLUENT FROM SAID SYNTHESIS ZONE AT SUBSTANTIALLY SAID SYNTHESIS TEMPERATURE AND PRESSURE, COOLING SAID EFFLUENT EXCLUSIVELY IN INDIRECT HEAT EXCHANGE WITH WATER TO A TEMPERATURE WITHIN THE RANGE OF ABOUT 350* TO 470* F. AT WHICH SUBSTANTIALLY NO LIQUID CONDENSATION TAKES PLACE, FURTHER COOLING SAID EFFLUENT BY ADDING THERETO A MINOR AMOUNT OF A HEAVY OIL BOILING ABOVE SAID LATTER TEMPERATURE, PASSING THE RESULTING MIXTURE OF LIQUID AND VAPORS IN INDIRECT HEAT EXCHANGE WITH SAID GAS MIXTURE OF NOT BELOW ABOUT 175* F. TO REHEAT SAID MIXTURE TO ABOUT 250-300* F., AND FINALLY CONDENSING NORMALLY LIQUID PRODUCTS FROM SAID EFFLUENT. 